Amplifier circuit



April 10, 1945.

Filed Nov. 18, 1942 2 Shets-Sheet 1 D/liEC770/V/YL GYROSCOPE ID P051770 Isnnentor RUBBER April 10, 1945. W, J HE 2,373,241

AMPLIFIER CIRCUIT Filed Nov. 18, 1942 2 Sheets-Sheet 2 Enocutor WILL/19M r1 $7540 attorney Patented Apr. 10, 1945 AMPLIFIER CIRCUIT William J. Field, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn.,'a corporation of Delaware Application November 18, 1942, Serial No. 466,010

6 Claims. Cl. 179171) directional energy, it is customary to utilize an alternating source, and to provide a. rectifier and filter circuit for obtaining unidirectional energy therefrom. Most rectifier circuits have a considerable alternating component in their output, and the filter circuit is utilized to remove this alternating component so that the amplifier may be supplied with purely unidirectional electrical energy. Absolutely perfect filter circuits are, however, unknown. Furthermore, the more perfeet a filter circuit is, the more complicated and expensive it is likely to be. 1

It is therefore an object of the present invention to provide a circuit arrangement wherein a relatively simple filter circuit may be used between 9. rectifier and an amplifier circuit, and:

wherein improved means are provided to prevent the appearance of any substantial alternating component in the final stage of the amplifier.-

Another object of the present invention is to I provide a power supply circuit for a multiple stage amplifier, in which two stages of the amplifier are connected to electrically spaced points in the power supp y circuit, and in which .the attenuation of the alternating component in the power supply'circuit between these two points are proportioned to the gain in the amplifier circuit. A still further object is to provide, in an amplifier and power supply circuit of the type described, means whereby the phase shift between sentation of a control system wherein the amplifier circuit of Figure 1 may be used, and

Figure 3 is an electrical wiring diagram of a modified form of amplifier circuit embodying the principles of my invention.

Referring now to Figure 2, there is shown a system for controlling the movements of the rudder of an aircraft in accordance with the deflection of a directional gyroscope, diagrammatically indicated at ill, from a normal position. The gyroscope i0 is indicated as rotating a shaft ll whenever the aircraft upon which the gyroscope is mounted changes its direction. Fixed on the shaft ii is a slider [2, which cooperates with a slidewire-resistance it. The slider i2 and the resistance It together form a control potentiometer it.

The resistance It is connected in an electrical network ii, of the Wheatstone bridge type. The network i5 also includes a slidewire resistance It with which is associated a slider H. The resistance l6 and slider I! together form a follow-up potentiometer I8. The network it is supplied with electrical energy from a transformer secondary winding I54; whose terminals 20 and II are connected through conductors 22 and 23, respectively, to the left and right terminals of resistances I 3 and It. The sliders l2 and I1 form the output terminals of the network It. The slider i1 is fixed on a shaft 24 for rotation therewith. The shaft 24 also carries a pulley 28 and a gear 26. A cable 21 runs over the pulley II. This cable 21 may be the conventional control cable used in aircraft for positioning the rudder.

The gear it engages a pair of gears 30 and 3|,

. which are fixed on shafts 32 and 33, respectively.

the aforesaid two points in the filter circuit is 48 supplementary to the phase shift occurring between the amplifier stages.-

them-inciplesofmyinvention.

mm'czisasomewhat Y amplifier and power supply circuit embodying and g The shaft 32 is connectable through an electrically operable clutch device schematically indicated at II to a driving shaft 35. Similarly. the

' shaft 3: is connectable by an electrically operable clutch device Ii to a driving shaft 31. The shafts 3i and 31 carry gears .38 and 39, respectively,-

which mate with each other so that the shafts 3i and I1 rotate in opposite directions. The gear II engages a gear 4i which is driven by a continuously running motor 42.

The motor 42 may be supplied with electrical energy from any suitable source, as for example a battery 43. An energizin circuit for motor llmaybetracedfromtheuppertermlnalofbat= tery 48 through conductors ll and II, motor", a conductor ll, ground connections 41 and I,

conductor tothelower terminaloibat- 1 ter! 3 I van reple- I The battery II also supplies electrical energy to a converter 5|, which may be of any conventional type, and serves to supply alternating electrical energy to an amplifier 52,- which is described in detail in Figure 1. v The direct current input circuit for converter 5| may be traced from the upper terminal of battery 43 through conduc, tors -44 and 53, converter 5|, a conductor 54;

ground connections 59 and 49, and conductor 49 to the lower terminal of battery 43. The con-. verterIiI supplies alternating electrical energy through conductors 59 and 51 to power input ter I minals 59 and 59 of implifier 52.

The slider I2 is connected through a shielded conductor 9| to an input terminal 92 of amplifier 52. The slider II, which serves asthe othera terminal 91,01 amplifier 52, an internal connection in amplifier '52, a terminal 59, a conductor 99, clutch 34, a conductor I0, ground connections II and 49, and conductor 49 to the lower terminal of battery 43. The energizing circuit for clutch 39 may be traced from the upper terminal of battery 43 through a conductor 13, a terminal I4 of. amplifier 52, an internal connection in amplifier 52, a terminal I5, a conductor 19,-

clutch 39, a conducton'l'l, ground connections I8 and 49, and conductor 49 to .the lower terminal of battery 43.

Suitable switch means may be provided for shutting down the entire system when not in use.

Also, limit switch means may be provided for se- I lectively preventing energization of one or the other of the clutches when the follow-up potentiometer, or the rudder, reaches the end of its range of travel. A suitable switching arrangement is shown, for example, in the co-pending application of Willis H. Gille, Serial No. 447,989,. filed June 22, 1942.

Referring to Figure 1, there are shown the details of the amplifier circuit 52. This amplifier ance 90, terminal 65, and ground connections 49 and 93 to cathode 91. The output circuit of stage 90 may be traced from a conductor 94, which serves as the positive terminal of the output circuit power supply, through a load resistance 99,

anode 85,'and cathode 91 to ground at 33, the

ground connection serving as the negative terminal of the output circuit power supply.

The second amplifier stage 8| includes a triode 99 having an anode 91,- a control electrode 99, a

cathode 99, and a heater filament I09. The triodes 94 and 99 may be. for example, the two halves of a single 7F! twin triode. The input circuit of the stage 9| may be traced from the control electrode 99'through a resistance MI, a resistance I02, a resistance I03, and a condenser I04 in parallel therewith, and ground connections I09 and I09 to cathode 99. The output circuit of stage 9| may be traced from positive supply terminal 94 through a load resistance I I I, an-

ode 91, and cathode 99 to ground at I09.

A pair of resistances'I I2 and I I3 areconnected between positive power sup ly terminal 94 and ground at H4. The resistance H3 is provided with an adjustable tap II5, and the latter is connected through a resistance II9 to the lower terminal of resistance I02 in the input circuit of may be traced from the lower terminal of resist-p stage 8|. This connection servesto provide a positive bias potential for this input circuit. An' additional positive bias potential may be appliedto this input circuit through a connection which ance' I02 in the input circuit through a conduc-v tor II I, either through conductor II9, contact H9, and switch arm I to a conductor I24, or through conductor I2I, contact I22, and switch arm I23 to conductor I24, and-thence through a variable resistance I25 and fixed resistance I29 to a terminal I80 in the power supply circuit 93.

.The terminal I90 is located at a point in the power supply circuit 93 which is positive with re= spect to ground. Variations in the potentialot anode 95 caused by variations in the output cur-. rent of the stage 90 are coupled .tothe input circuit of stage 8| through a blocking condense I21 and a conductor I29.

comprises a first preliminary voltage amplifica- 7 tion stage 90,'a second preliminary voltage amplification stage 9|, and a final power amplification stage 82. The amplifier 52 also includes a power supply circuit, generally indicated at 93, which supplies power to the preliminary stages for the second'stage 9| and the final stage 92.

The first amplification stage 90 includes an electrical discharge device, shown as a triode 94, which maybe, for examp'le, one-halfl of a twin triode of the type known commercially as type The final power amplification stage 92 includes a twin triode I30, which may be of the type commerciallyknown as type 7N7. The twin triode I30 includes two separate triodes I3I and I33. The triode I3| includes an anode I33, a control electrode I34, a cathode I35, and a heater file- 90 and 9| and provides suitable biasing potentials ment I39, The triode I32 includes an anode I31, a control electrode I39, a heater filament I40. 4

The power amplification stage 92 includes a common input circuit for both the triodes I3I and I32. This common input circuit may. be traced from either control electrode I34 or control electrode I38 through a conductor I42, a conductor I43, a movable tap I44, a portion 0! a resistance 7E7. The triode 94 includes an anode 95, a control electrode 99, a cathode 91, and a heater filament 99. 1 A resistance 99 is connected across the input terminals 92 and 99 o! amplifier 92, so that any signal potentialoccurring between these terminals' causes a corresponding current flow through resistance 90. The resistance 99 is providedwithv an adjustable tap 9I, which serves in a well known manner to control the gain of the amplifier 92;

The'input' circuit oramplifier stage 90may be traced from control electrode 99 through a I45, and ground connections I49 and I41 flto cathodes I and I39, Variations in the potential oi anode 91 caused by variations in the output :current of the second amplifier stage 8| are transmitted to the common. input circuit of the final stage 92 through a blocking condenser I49 and a conductor I49 to conductor I42 in the-common input circuit. The resistance I45 islso connected in the power supply circuit 93 that the'tap I44 is negative with respect to ground. The setting of tap I44 with respect to resistance I49 therefore determines a negativev bias potential shielded conductor 92, tap;9l,"ap rti p fr ist- 79 appl ed to the common input circuit of final cathode I39, and a Y stage 52 and hence determines the normal current now in the output circuits of that stage.

The output circuit of final stage 52 is divided into two branches, each of which includes the anode and cathode of one of the triodes 151 and 152. Both branches of the output circuit of stage 52 are supplied with alternating electrical energy from a secondary winding 151 of a transformer'152. The transformer 152 also includes a primary winding 153 and two additional secondarywindings 155 and 155. The upper branch of the output circuit of final stage 52 may be traced from the upper terminal of secondary winding 151 through a winding 155 of a relay 155 and a condenser 151 connected in parallel with winding 156, anode 155, cathode 155, and ground connections 151 and 155 to a center tap 161! on transformer secondary winding 151. The lower branch of the final stage output circuit may be traced from the lower terminal of secondary winding 151 through a winding 151 of a relay 152 and a condenser 163 in parallel with the winding 151, anode 151, cathode 155, and

ground connections 141v and 155 to center tap 155 on winding 151.

The two branches of the output circuit of final stage 82 may be conductive on opposite half cycles of the alternating energy supplied by the winding 151, that is, the triode 131 may be conductive during the half cycle when the upper terminal of winding 151 is positive with respect to the center tap 150, while the triode 152 may be conductive during the half cycle when the lower terminal of secondary winding 151 is positive with respect to center tap 160. The secondary winding 154 of transformer 152 is con nected through the terminals 25 and 21 to the network 15 (see Figure 2). Therefore, any signal which appears between the output terminals of the network 15 is of the same frequency as the energy supplied to the final output stage 52. In accordance with the well known characteristics of alternating current bridge circuits, it will be understood that the time phase of such a signal depends upon the direction of unbalance of the network 15. If the phase of the signal is such that the control electrodes 134 and 155 are positive when the upper terminal of secondary winding 151 is positive, the current flow through triode 131 is increased above the normal value determined by the setting of tap 1 on resistance 155, while if the phase of the signal is such that the control electrodes 1 and 155 are positive when the lower terminal of secondary winding 151 is positive then the current flow through the triode 152 is increased. Condensers 151 and 155 operate to maintain energization of the relay windings 155 and 151, respectively, over a period longer than the hall cycles during which the tri- I odes associated with the respective relays are conductive. During the half cycle when a particular triode is conductive, the output circuit current fiows through the relay winding and also charges the condenser. when the triode is non-conductive. the condenser discharges through the relay winding, thereby maintaining the current flow.

Relay 155 includes, in addition to the winding 155, the switch arm 125 Previously mentioned, and a switch arm 155 which cooperates with a stationary contact 155. Both the switch arms 125 and 155 are biased, by means'not showmto the circuit opening position and are moved to circuit closing position upon suiilcient energizetionof relaywinding 155.

During the half cycle- The relay 152 similarly includes, in addition to winding I51 and the switch arm 125 previously mentioned, a switch arm 151 which cooperates with the stationary contact 155. Both switch arms 125 and 151 are biased to the circuit opening position and are moved to their circuit closing position upon suflicient energization of winding 151.

The power supply circuit 53 is energized from secondary winding 155 of transformer 15!. The power supply circuit 83 includes a twin diode 115 which may, for example, be of the type commer-- cially known as type 7Y7. The twin diode 115, which serves in the power supply circuit 55 as a full wave rectifier, includes a first diode 111 having an anode 112, a cathode 113, and a heater The current supply to the output circuit of stages 55 and 81 passes from the terminal 155 through a filter network 190 comprising a choke coil 151 and condensers 182 and 183 connected between opposite. terminals of the choke coil 151 and ground. After passing through the filter network, the current flows along conductor 154 to conductor 94 which serves as the positive power supply terminal for the output circuits of stages 55 and 51. The various ground connections serve as the negative power supply terminals of these output circuits. The current supplied by the rectifier fiows through the various amplifier output circuits and ground connections to ground connection 155, and thence through resistance 155 andconductors 185 and 186 to a center tap 151 on transformer secondary winding 155. It should be noted that the direction of current fiow through resistance is such as to make its left terminal positive with respect to its right terminal, as indicated by the legend in the drawinss.

A filter condenser 188 is connected between terminal and center tap 155.

In order to aid those skilled in the art in constructing an amplifier in accordance with my invention, the followin table is appended, giving values of the various resistances and condensers used in one embodiment of my invention:

Reierenoe character Quantity c. resistance, so mm in ductnnce.

1B2. )imiaohnd. 158. .05 Miami. 18. .05 mic-chad.

The heater filaments 88, I00, I36, I40, Ilfland I'll may be connected to any suitable source of electrical energy' (not shown) Operation The operation of the amplifier circuit 52 and of thesystem shown in Figure 2 are described in detail in the copending application of Willis l-l; Gille, Albert P, Upton, and William J. Field, Serial No. 466,088, filed on even date herewith.

It is believed sufiicient for the purposes of the present-application to, state that the amplifier 52 operates to cause intermittent energlzation of one. of the relays I58 and I6: when the signal impressed upon its input terminals 62 and. 65 is small in value. When the signal increases in magnitude, the particular relay selected is con-- tinuously energized. As previously mentioned,

therelays are selectively energized in accordance with the phase of the alternating signal theoretical considerations'or by direct measurev ment. Since the filter circuit I90is very simple in construction, and therefore imperfectas a filter, an alternating component passes through the conductors I84 and 94 to the output circuits of thestages 80 and 8|.

'ponent so impressed on stage 80 is amplified-in tap I81 of transformer winding I55, and are stage 8| and transm tted through blocking condenser I48 to the input circuit of final stage 82. The-alternating component so impressed on stage 8|, although not amplified, is likewise transmitted through blocking condenser I48 to the input circuit of final stage 82. Due to the phase shift The alternating combetween stages 80 and 8|, these two alternating components add vectorially, and not algebraically, but it is believed to be clear that the total alternating component passed through blocking condenser I48 is considerably larger, due to the amplification of one of its components, than the alternating component existing between terminal I9I of filter I90 and ground.

The input circuit of final stage 82 is connected to tap I, which is associated with the power supply circuit 83 at a point where the alternating component of current flowing in the power supply circuit is much greater than the alternating component existing at terminal ISI. It maybe notedthat a portion of the total alternating c'omponentinthe output of rectifier I10 is by-passed from the filter I90 and from the resistance I65 byv the condenser I88. Furthermore, the condensers- I82 and I83 by-pass con.- ditional fractions of the alternating component in' the rectifier output, which additional fractions therefore do not pass through the output circuits of stages 80 and 8|. These additional components do however. pass through ground connection I46 and res stance I45 to the center therefore impressed through tap I to the com-. mon input circuit of the final stage 82,

I have found,.that by properly proportioning the attenuation of the alternating component in the filter network I80 to the gain in the amplifier stage BI, the magnitude of the alternating component impressed on the common input'circuitci final stage 82 through tap I may be denser I48. Furthermore, by properly the elements in the filter circuit I90 sons to which reach the input circuit of the final stage substantially opposite in phase. If these-twoalternating components are made equal in magnitude and opposite in phase, they cancel each other out and have no efiect'on the final stage.

output circuit.

While it is entirely possible retical analysis of the-relationship between the amplifier gain and the loss in. the filter circuit.

and a similar relationship between the phase shifts in-the amplifier and filter circuit, I have found it more convenient from a practical standpoint to determine the. various values of circuit elements to be employed in any given case by empirical methods. The values given in the table previously set forth show values of the vari o'us circuit elements which have operated satis-- factorily in one embodiment of my invention.

Figure 3 In Figure 3, is shown a somewhat different amplifiercircuit embodying my invention. This amplifier circuit, generally indicated lit-200, in

cludes three preliminary voltage amplification 7 stages 20I, 202, and 20.3 and a final power ampli fication stage 204. The amplifier 200 also in cludes apower supply circuit 205 including a full wave rectifier 208and a filter circuit 201,

In the amplifier 200'the final stage 204 is'not supplied with a biasing potential, or infact with arm potential from thepower supply circuit 208.

It is therefore necessary, in applying my invention to this circuit, to proportion the alternating component applied from the rectifier 208 to the last preliminary stage;203 in such a manner that it is equal in magnitude and opposite'in phase to th alternating components reaching the output circuit of stage 203 through the previous stages rm and 202.

The rectifier 206 has a positive terminal 2I0 and a negative terminal 2I l.' Thefilter'circuit 201 is divided into two sections, one between rectifier output'terminal 2I0 and a terminal 2I2, and the other section between terminals 2I2 and 2I3. The attenuation of the alternating component and the 'phase shift in the filter section between terminals 2 I2 and 2I3 should be proportioned to the gain and phase shift in the amplifier circuit 202, in order to reduce asmuch as possible the resultant alternating componenttransmitted to the final stage 203. The alternating component attenuation and phase shift in the section of the filter circuit between terminals 2I0 and 282 may then be proportioned so that the alternating component supplied directlyto the output circuit of stage 203 is of the proper magnitude and phase to cancel out the alternating component transmitted to stage 203 from the previousstages.

While I have shown and described certain preferred embodiments of my invention, other modi-, fications thereof will occur to those skilled in the Y art.v and I therefore wish my invention to be circuit of the final stage through blocking conlimited only by the appended claims.

I claim as my, invention:

1. An amplifier circuit, comprising in combine tion, aplurality of cascaded am lifier stages, each stage havingan input circuit and an. output cirfcuit, first power for supplying,

to developja thee aavaas'r alternating voltage to the output circuit of said final stage, second power supply means for supplying a unidirectional voltage to the remaining output circuits, said second power supply means including a source of alternating electrical energy, rectifier means having an appreciable alternating component in its output potential, and a filter network, connections between said remaining output circuits and a first point in said filter network electrically remote from said rectifier means, and a connection between the input circuit of said final stage and a second point in said filter-network electrically closer to said rectifier means than said'first point, said filter network including impedance means connecting said two points, said impedance means having a characteristic such that the alternating component of potential introduced into said final stage through said last-mentioned connection is substantially equal in magnitude and opposite in phase to the vector sum of the alternating components trans- Knitted to said final stage through said amplifier stages.

2. An amplifier circuit, comprising in combination, a plurality of cascaded amplifier stages, each stage having an input circuit and an output circuit, first power supply means for supplying. an alterhating voltage to'the output circuit of said final stage, second power supply means for supplying a unidirectional voltage! to the remaining output circuits, said second power supply means including a source of alternating electrical energy, rec tifier means having an appreciable alternating component in its output potential, and a filter network; connections between said remaining output circuits and a first point in said filter network electrically remote from said rectifier means, and a connection between the input circuit of said final stage and a second point in said filter network electrically closer to said rectifier means than said first point, said filter network through said last mentioned connection is substantially equal in magnitude and opposite in phaseto'the vector sum of the alternating components transmitted to said last output circuit through the earlier amplifier stages.

4.-.An amplifier circuit, comprising, in combination, a plurality of amplifier stages, each having an'input and output circuit, means coupling said stages so as to invert the phase oi signal potentials transmitted therebetween, power supply means for said stages including a source of alternating electrical energy, rectifier means connected to said source, a filter network, said including firstimpedance means connecting said through said amplifier stages.

3. An amplifier circuit, comprising in combination, a plurality of cascaded amplifier stages.

7 each stage having an input circuit and an output circuit,. first power supply means for supplying an alternating voltage to the output circuit of said final stage, second power supply filter network comprising a condenser and a first substantially non-capacitive impedance connected in series with said rectifier and said power source, a second condenser and a second substantially non-capacitive impedance connected in parallel with said first condenser but not with said first impedance, means for applying a portion of the voltage across said second condenser to the input circuit of one or" said stages, the output circuit of said one stage being connected to the input circuit of. said final stage, and means for applying aportion oi the voltage across said first named impedance to the input circuit of said final stage, the values of said condensers and impedances being so chosen that the ripple introduced directly into the input circuit of said final stage from said source of power is cancelled out by the ripple introduced by said source of power into said input circuit from said one stage. a

5. An amplifier circuit, comprising, in combi nation, a plurality of amplifier stages, each having an input and output circuit, means coupling said stages so as to invert the phase of signal powith said first condenser but not with said first impedance, means for app ying a-portion of the voltage across said second condenser to the output circuit of a first of said stages and hence to the input circuit of a second of said stages, the

output circuit of-said second stage being connected to the input circuit of a final stage, and

means for applying a portion of the voltage across said first named impedance to the input circuit of said final stage, the-values of said condensers and impedances being so chosen that the ripple introduced directly into the input cirmeans for supplying a unidirectional voltage to the remaining output circuits, said second power supply means including a source of alternating electrical energy, rectifier-means having an .ap-

preciable alternating component in its output potential, and a filter network, connections between all'but the last inthe cascade of said re- 'maining output circuits and a first point in said filter network electrically remote ,from said rectiin; impedance means connecting said two points.

said impedance means having a characteristic such that the alternating component of poten-,

tial introduced into said last output circuit an alternating voltage from saidsource to the cult of said final stage from said source of power is cancelled out by the ripple introduced by said source of power into said input circuit from the first and second stages.

6. An amplifier-circuit, comprising, in combination, a plurality of amplifier stages, each having an input and output circuit, means coupling said stages so as to invert the phase of signal potentials transmitted therebetween, power supply means for said stages including a source of a1- ternating'electrical energy, means forapplylng output circuit of the final one of said stages, rec'- Itifier means connected to said source, a filter net-' work. said filter networkj comprising a con denser and a first suostantially non-capacitive impedance connected in series with; said recti- 56 2,978,241 he! and said power source and a second con- I denser and a second substantially non-capacitive impedance connected in parallel with said first condenser-but not with said first impedance, means for applying a. portion of the voltage across said second condenser to the output circuits of s first and a second of said stages, the

output circuit of said second stage being connected to the input circuit of. said 1 stage, and means for app 2' s; portion of the vol densers and impedances being so chosen :tiict time ripple introduced into the input circuit-5 oi 6 said final stage from said source. of power is conceiled out by the ripple introduced by said source of power into ssid input circuit irom the: first d second across said first nsmedimpedance to the input circuit oi said final stage, the values of said con- 

